2

Is there a working technique to execute XSS in modern browsers using a SVG file displayed on a web page with an <img src=""> tag?

I know a way to execute without <script> tag, but I don't know how to load a file using SVG or anything else, because XML breaks when I try using different tags to get my XSS working.

Is this actually possible?

2

No, it's not. Although SVG files can contain JS (see this), these will only get executed if:

  1. the user directly visits the .svg file in their browser
  2. the image is embedded within <embed> tags.

Modern browsers will never execute scripts in SVGs if it's within <img> tags.

And even in the two cases above, the server can provide CSP headers that stop the execution of such scripts.

  • A third edge case would be a bug in the SVG implementation. I think this has happened. – forest Jul 8 at 8:41
-1

SVG images can contain CSS, CSS are a possible injection point for XSS

See https://stackoverflow.com/questions/3607894/cross-site-scripting-in-css-stylesheets And https://code.google.com/archive/p/browsersec/wikis/Part1.wiki#Cascading_stylesheets

Which both point out

As a little-known feature, some CSS implementations permit JavaScript code to be embedded in stylesheets. There are at least three ways to achieve this goal: by using the expression(...) directive, which gives the ability to evaluate arbitrary JavaScript statements and use their value as a CSS parameter; by using the url('javascript:...') directive on properties that support it; or by invoking browser-specific features such as the -moz-binding mechanism of Firefox.

So, yes, you can use user controlled SVG's to execute script in the domain of the host page.

Using Content-Security-Policy you can restrict where you expect to find styles or script. Another thing you could try is serve these SVG's in a sandboxed cross-domain iframe.

  • 4
    Sorry, that's not correct. An SVG in an <img> tag will not execute active script code. Also, JS in CSS expressions doesn't work in any modern browser. – Arminius Jul 4 at 10:01
  • @Arminius Well, i've been testing SVG and CSS+XSS for 6 months now, i found that SVG XSS is still working with data URI's(found a way to make a double embedded execution today, and then it works in any page), not sure if it's a real security bug. And CSS+XSS can work but only on <style> tag and in the same page of the <div>. I found that some tags are being blocked, like document. and window., but alert and prompt yet works using the same technique i found some months ago. So it isn't so "impossible"! But it's really hard to test many codes to get it working. – Mega Jul 4 at 23:26
  • @Mega Script code in SVGs is possible. But script code in SVGs embedded via <img> is strictly not possible. (Unless you found a bypass that constitutes a severe security issue.) Also, injecting script code via CSS is not possible. That is, if I embed an image or a stylesheet of your choice on my site, you will not be able to execute any Javascript through that. – Arminius Jul 5 at 0:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.